The present invention relates to a seat weighing device, provided to a seat for a vehicle, for weighing a seat including the weight of a passenger on the seat.
As safety devices for improving safety of a passenger in an automobile, a seat belt device, an airbag device, and the like, are known. Recently, development of control devices for controlling these safety devices corresponding to the weight and the attitude of the passenger is being undertaken in order to further improve the performance of the seat belt or the airbag. For example, the control device adjusts the amount of the inflation gas or the inflation speed of the airbag, or adjusts the pretension of the seat belt, corresponding to the weight and the attitude of the passenger. Accordingly, there is the need to weigh the passenger on the seat, as well as the position of the center of gravity of the passenger.
In order to meet such a demand, a low-cost seat weighing device has been proposed for precisely weighing the seat such as, for example, Japanese Unexamined Patent Application Publication No. 2001-041813 (hereby incorporated by reference herein in its entirety).
FIGS. 7(A)–7(B) show partial views of the front portion of the seat weighing device disclosed in the aforementioned Japanese Unexamined Patent Application Publication No. 2001-041813, wherein FIG. 7(A) is a disassembled perspective view thereof, FIG. 7(B) is a cross-sectional front view of a pin-bracket portion thereof, and FIGS. 8(A), 8(B), 8(C), and 8(D) show partial views of the front portion of the seat weighing device shown in FIGS. 7(A)–(B), wherein FIG. 8(A) is a plan view thereof, FIG. 8(B) is a cross-sectional view along the longitudinal direction thereof, FIG. 8(C) is a cross-sectional view taken along line C—C in FIG. 8(B), and FIG. 8(D) is a cross-sectional view taken along line D—D in FIG. 8(B).
As shown in FIGS. 7(A) and 7(B), and FIGS. 8(A) and 8(B), a conventional seat weighing device 9 comprises a long and narrow base 21 serving as a base component thereof. The base 21 is to be mounted on the vehicle body, extending long in the longitudinal direction thereof, and the base 21 formed of a U-shaped pressed steel frame is mounted with the open side facing upward, wherein both the left and right ends of a bottom plate 21c of the base are bent perpendicular thereto so as to form side plates 21a and 21a′ erected on the bottom plate 21, as shown in FIGS. 8(C) and 8(D).
Each of the side plates 21a and 21a′ of the base 21 include two pin openings 21e and 21g arrayed in the longitudinal direction of the base 21. Note that the pin openings 21e and 21g are formed on both the side plates 21a and 21a′ so as to face the corresponding pin openings. The pin openings 21e closer to the front end are formed at positions around ⅛ of the entire length of the base 21 away from the front portion of the base 21 along the longitudinal direction thereof. The pin openings 21e are formed in the shape of a slot with the major axis perpendicular to the bottom plate 21c as shown in FIG. 7(A). The ends of a bracket pin 27 are inserted into the slots 21e. Furthermore, retainers 33 are secured to both the left and right ends of the bracket pin 27. The bracket pin 27 is fixed to the slot 21e by the retainers 33.
However, the bracket pin 27 is inserted into the slots 21e with a gap in both the horizontal and vertical directions, i.e., the bracket pin 27 is not in contact with the inner faces of the slots 21e in the normal state. However, in the event that an excessive load is applied to the seat weighing device 9 (specifically, the pin bracket 25), the bracket pin 27 moves downward and comes into contact with the lower edge of the slot 21e, and accordingly, the excessive load does not affect a load sensor 50 disposed on a sensor plate (spring member) 51. That is to say, the bracket pin 27 and the slots 21e form a part of the restricting mechanism for restricting the maximal load applied to the sensor plate 51. Note that the bracket pin 27 generally serves as a member for transmitting the weight of the seat applied to the pin bracket 25 to an arm 23.
Furthermore, the pin openings 21g are formed at positions somewhat away from the slot 21e toward the middle portion of the base 21 (specifically, at positions approximately 1/10 of the entire length of the base 21 away from the slot 21e toward the middle portion). A base pin 31 passes through the pin openings 21g. The base pin 31 is disposed so as to be introduced between both the left and the right side plates 21a and 21a′ of the base 21. Furthermore, retainers 33 are secured to both the left and right ends of the base pin 31 so as to fix the base pin 31 to the base 21. Note that the base pin 31 serves as a shaft around which the arm 23 is turned.
The arm 23 is formed of an elastic member, and is disposed within the base 21. The bottom plate of the arm 23 is formed in the shape wherein one end thereof closer to the middle portion of the base 21 is formed in the shape of “V” extending in the horizontal direction (V-shaped portion 23h), and the other end thereof closer to the front end of the base 21 is formed in the shape of a rectangle. Both the left and the right ends of a half part of the arm 23 closer to the front end of the base 21 are bent upward perpendicular to the bottom plate of the arm 23 so as to form side plates 23a. On the other hand, the V-shaped portion 23h is formed of a simple flat plate. The side plates 23a are disposed within the base 21 along the side plates 21a thereof. Note that the side plates 23a and 21a are disposed with a gap therebetween.
Each of the side plates 23a of the arm 23 include two pin openings 23c and 23e, as well. The bracket pin 27 passes through the pin openings 23c formed closer to the front end of the base 21. The bracket pin 27 hardly exhibits any sliding movement on the pin openings 23c. On the other hand, the base pin 31 passes through the pin openings 23e formed closer to the middle portion of the base 21. The base pin 31 serves as a center around which the arm 23 is turned, and accordingly, the base pin 31 exhibits sliding movement on the pin openings 23e corresponding to turning of the arm 23. Note that doughnut-shaped spacers 35 are fit to both the ends of the base pin 31 between the side plate 21a of the base 21 and the side plate 23a of the arm 23.
The V-shaped portion 23h of the arm 23 is formed with generally half of the entire length of the arm 23. The left and right ends of the V-shaped portion 23h are forked so as to extend toward the middle portion of the base 21 in the longitudinal direction, and are formed narrow closer to the middle portion. Action portions 23j at the tips of the V-shaped portion 23h of the arm 23 are introduced between a blade 41a of an upper half arm 41 and a blade 42a of a lower half arm 42. The lower face of the main body of the upper half arm 41 and the upper face of the main body of the lower half arm 42, formed flat, are fixed to a sensor plate 51 so as to be fit flush with the surface thereof with a screw 43.
Upon a load being applied to the pin bracket 25, the load is applied to the arm 23, and as a result, the arm 23 is slightly turned (with the maximal turning angle of 5°) so as to transmit the load to the sensor plate 51 from the action portions 23j through the upper and lower half arms 41 and 42. As shown in FIG. 9, the load sensor 50 is mounted on the sensor plate 51. Of four deformation resistors forming the load sensor 50, two deformation resistors 54a and 54b thereof are disposed so as to detect the tensile strain, and the other two deformation resistors 54c and 54d are disposed so as to detect the compressive strain. Note that these four deformation resistors 54a, 54b, 54c, and 54d, are disposed in that order along the line passing through the center of the sensor plate 51 in the longitudinal direction thereof.
Furthermore, the aforementioned four deformation resistors 54a, 54b, 54c, and 54d, are electrically connected so as to form a bridge circuit. The pin bracket 25 is formed generally in a cross-sectional shape of “U” with the open side facing downward as shown in FIG. 8(C). Note that the pin bracket 25 is formed with length of around 1/20 of the base 21 in the longitudinal direction, which is not so long. Furthermore, the upper face 25a of the pin bracket 25 is formed flat so as to mount a seal rail 7. Note that the seat rail 7 is fixedly connected to the pin bracket 25 with screws or the like. Furthermore, the sensor plate 51 is fixed to a column 63 erected on the middle portion of the bottom plate 21c of the base 21 with nuts 68, and fastening members 69 such as screws, bolts, or the like.
Both left and right side plates 25b of the pin bracket 25 extend downward, and both the lower ends thereof are bent inward. The side plates 25b are disposed so as to be introduced between the side plates 23a and 23a′ of the arm 23 with a predetermined gap. Furthermore, the side plates 25b include pin openings 25c. Note that the bracket pin 27 passes through the pin openings 25c. The pin openings 25c are formed with a greater size than the diameter of the bracket pin 27. The gaps between the pin openings 25c and the bracket pin 27 absorb the margin of error in the size of the seat and vehicle, and unintended deformation.
A spring plate 29 is disposed so as to be introduced between both the left and right side plates 25b of the pin bracket 25 and both the left and right side plates 23a of the arm 23. The spring plate 29 has a spring seat including openings for fitting the bracket pin 27 with a gap. The spring plate 29 forms a centering mechanism for forcing the pin bracket 25 toward middle portion. Such a centering mechanism forces the pin bracket 25 to be slidably positioned at a position as close to the middle as possible.
With the seat weighing device 9, the seal rail 7, pin bracket 25, the arm 23, the base 21, the seat bracket 11, and the like, form a connecting mechanism between the seat and the vehicle.
With the seat weighing device disclosed in Japanese Unexamined Patent Application Publication No. 2001-041813, recesses are formed at the regions between a pair of the deformation resistors 54a and 54c, and between the other pair of the deformation resistors 54b and 54d, forming the load sensor 50, on the sensor plate 51, so that the sensor plate 51 readily flexes (deforms) around these regions, thereby stabilizing the sensitivity of the load sensor, but there is the need to perform precision machining for the sensor plate, leading to a problem of high costs.
On the other hand, the four deformation resistors 54a, 54b, 54c, and 54d, are disposed in that order along the line passing through the center of the sensor (i.e., the center of the fastening member 69) in the longitudinal direction of the sensor plate 51, and accordingly, are not disposed at positions with the same distance from the center of the sensor. Accordingly, in the event that rapid change in the temperature of the surroundings occurs, the four deformation resistors 54a, 54b, 54c, and 54d, may not immediately reach the same temperature due to heat transmitted to the sensor plate 51 through the fastening member 69 secured at the middle portion of the sensor, leading to a problem that the bridge formed of the four deformation resistors may lose balance thereof.